This invention concerns a method for supplying weft threads into the shed of a weaving machine, in particular of weaving machines of the type where weft threads are inserted in the shed by means of a transport fluid, and also a device which uses this method.
It is known that in weaving machines of this type, the relation between the insertion of a weft thread and the shed formation must meet two major conditions. The first condition is that the shed must be sufficiently opened and correct at the moment when the weft thread is inserted in the shed, in a way that it is impossible for the inserted weft thread and the warp threads to become entangled. A second major condition is that the weft thread must be kept taut in the shed before it is beaten up and before the shed is closed.
As known, the shed formation, i.e. the opening of the shed and the creation of a correct shed, depends on different factors. A first factor is the weave pattern, i.e. the moving pattern of the harnesses according to which different sheds are successively formed, and which are repeated per sequence.
Two other major factors which characterize the shed formation are the type of warp threads used and the warp count.
It is possible that during the shift of the harnesses, a number of warp threads will become temporarily entangled until the warp and in particular, the harnesses in question are sufficiently removed from each other again, thus keeping the warp threads taut. This possible entanglement depends on the two major factors listed above. This means, for example, that in a very regular weave pattern in which smooth warp threads are used, the shed will open very regularly, and the insertion of weft threads can start with a very small opening angle of the shed. In that case, the time available for the weft insertion is relatively long.
On the other hand, if the formed shed can only reopen itself with difficulty, meaning that the shed requires more time than usual to open itself sufficiently, which can imply a difference of 20 crank angles, the time available for the weft insertion is substantially shorter. Also, a higher weft insertion speed is required.
It is known that in weaving machines, a weft insertion never starts earlier than the moment when the moot difficult shed to be formed is sufficiently opened. If in a certain weave pattern, only one slowly opening shed occurs, the insertion of all weft threads will nevertheless therefore depend on the one slowly opening shed. This is disadvantageous in that a large number of weft threads are inserted at a higher speed than necessary, which increases the consumption of air. Moreover, most weft threads are put under a heavier strain than is strictly necessary during the weft insertion, which substantially increases the chance of weft breaks.